The previous post is mistaking the /z/ sound with that at the beginning of "think" - sorry, I don't know how I can write that phonetic symbol here (in Spanish the written letter "z" is pronounced as that sound in "think", at least in the areas the previous poster has stated, but it has nothing to do with the sound /z/, which for us sounds as /s/). We always pronounce the letter "s" in the same way, with no difference between /s/ and /z/ (although many Latin American friends have told me that in Spain we pronounce an "s" sound much stronger than in America).
Until some years ago there were different sounds for /b/ and /v/ in Spanish, but now only a few people use them, and it's considered archaic and incorrect as far as I know (we only use the sound /b/ now). In Spanish the letter "h" is silent, so when we must aspirate it (like in "house") we tend to exaggerate it, and say it almost as our "j" (a sound I'm unable to explain!) Another thing that helps spot a Spaniard speaking English is the difficulty in pronouncing words like "Spain" without saying an "e" before the "s". There are other consonant sounds that do exist in English but not in Spanish, like "sh" (which is not difficult) or the "j" in "joy", but I'd say the main difficulty for a Spaniard speaking English are vowels, owing to our tendency to use only five vowel sounds, as Novalee said. All of this said, there are Spaniards who speak other language apart from Spanish who use more vowels. I'm thinking here about the Catalan. In Catalan, "a", "i" and "u" are the same as in Spanish, but there are two different "e" and "o" sounds, and another vowel just between "a" and "e", so there are eight vowel sounds, which makes a Catalan speaking English less hard than, say, a Castillian.
Novalee, are those books and links you talked about also useful for us Spaniards trying to make English sound as such? If so, I'd be very interested in you telling us more about them!